Atoms and Particles

Particle physics is a journey into the heart of matter.

Everything in the universe, from stars and planets, to you and the chair that you're sitting on, is made from the same basic building blocks - particles of matter. Some particles were last seen only billionths of a second after the Big Bang. Others form most of the matter around us today.

Particle physics studies these very small building block particles and works out how they interact to make the universe look and behave the way it does.

How small is small?

Really small...

Think about the width of a human hair, one of the smallest things we can see – twenty of them placed side by side fit across one millimetre.

If we use a microscope to look inside a hair we see cells, which are formed from molecules. Each molecule is made up of a collection of atoms. We know that everything is formed from various types of atoms and that atoms are really small – you can fit a hundred thousand of them across a human hair.

But particle physics doesn’t stop there – we can see right inside the atom.

We see that atoms consist of a nucleus, ten thousand times smaller than the atom, surrounded by a cloud of electrons. The nucleus is a collection of particles called protons and neutrons. And inside protons and neutrons we find particles called quarks. Quarks are so small that we haven't yet been able to measure how big they are - we just know that they are at least ten thousand times smaller than the nucleus. They are so small that we treat them like mathematical pinpoints in our theories.

Zooming down in scale from a person to a fundamental particle like a quark or an electron is like shrinking the diameter of the whole earth to the size of a 5p coin. And then shrinking the 5p by the same amount again. This is what we mean by really small.

How do we do particle physics?

We recreate the conditions just after the Big Bang, when particles roamed freely through the Universe. We do this with powerful particle accelerators which accelerate particles close to the speed of light and smash them together. Particle physicists then look at what happens in the high energy collisions.

Particle physics is a bit like trying to find out how a watch works by bashing together two very expensive Swiss watches and then learning to rebuild them from all the bits of glass, cogs and springs. In place of Swiss watches we use particles so small that you could fit about ten thousand million of them across a watch face, and despite their tiny size, the collisions between these particles have as much energy as a large aeroplane taking off!